1) Field of the Invention
This invention relates to an SDH transmission unit for use with a network based on an SDH (Synchronous Digital Hierarchy) transmission system, and more particularly to an SDH transmission unit having a function as an ADM (Add-Drop Multiplexer).
2) Description of the Related Art
In an SDH transmission network (called SONET (Synchronous Optical Network) in the North America), high speed (source) networks which handle transmission (signal) frames of a predetermined transmission capacity (rate) of OC-N [Optical Carrier-level N: N=192 (approximately 10 Gb/s)/48 (approximately 2.4 Gb/s)/12 (approximately 600 Mb/s) and so forth) are implemented at present, and as a network application (network configuration) of it, for example, such terminal/linear, regenerator, ring [UPSR (Unidirectional Path Switched Ring)/BLSR (Bidirectional Line Switched Ring)] as shown in FIGS. 47 to 49 are available.
Referring to FIGS. 47 to 49, an ADM (SDH transmission unit) 100 having a main function of time slot assignment (TSA) of performing Add/Drop/Through processing in accordance with a line (signal) unit mapped to an OC-N signal frame mentioned above uses functions corresponding to such various applications as mentioned above so that the various applications can be applied by the single unit.
Where, for example, a high speed side line (OC-N) has a ring (UPSR) configuration as shown in FIG. 50, an ADM (node A) handles (accommodates) a line capacity for a sum total (=N channels) of channels (STS-1xc3x97n) allocated to communication among nodes (stations) B, C and D on the ring, and adds the same signal to signals in the EAST/WEST directions of the ring or selects one of same signals sent from the EAST/WEST directions to the ADM (node A) as a termination side node with respect to the node C which has a higher line quality and drops a pertaining signal channel (low speed line signal) to the low speed line (tributary) side.
A tributary block (TB) which performs processing of low speed side lines (OC-N/4, N/16, N/64 and so forth) can apply various applications such as a ring configuration similar to that on the high speed line side described above and a 1+1 redundancy configuration of the work/protection systems. Therefore, the TB is constructed taking an interface between various functioning boards (units) into consideration which is used to satisfy accommodation compatibility of interface (IF) units corresponding to various transmission levels (capacities) or applications.
In particular, for example, as shown in FIG. 51, a TB 200 has a plurality of IF units (IF boards (cards)) 300 for performing production/termination processing of OC-n transmission frames corresponding to various transmission levels (OC-n: when n less than N and N=192, for example, n=48/12/3 and so forth) of low speed side lines. Where the IF boards 300 accommodate low speed lines (tributary networks) of a 1+1 redundancy configuration, they are used for work units/protect units, but where the IF boards 300 accommodate low speed lines of a ring configuration, they are used for EAST/WEST side transmission units.
Each of the IF boards 300 includes, for a transmission line (line: OC-n level) input signal, an O/E (opto-electric) conversion section 301, a frame synchronism protection section 302, a descrambling section 303, an SOH reception processing section 304, a byte demultiplexing section 305, a supervision section 306 for various alarms such as an AIS and transfers a signal demultiplexed from a received OC-n transmission frame to a routing block (RB) 400 which is positioned in the next stage and performs low speed side line time slot assignment.
On the contrary, each of the IF boards 300 includes, for a signal transferred from the RB 400 after low speed side time slot assignment (Add assignment), a byte multiplexing section 307, an SOH insertion section 308, a scrambling section 309, an E/O conversion section 310, a BIP (Bit Interleaved Parity) processing section 311 and so forth and performs multiplexing of the Add assigned signal into a transmission frame (OC-n level), addition of an SOH to the multiplexed transmission frame, scramble coding, E/O conversion and so forth to produce a transmission line (OC-n level) output signal.
It is to be noted that the RB 400 performs switching operations (switching/bridging and so forth) of the low speed side lines suitable for the various applications described above. For example, the RB 400 has a function 40a of performing, where the 1+1 redundancy configuration is employed, a line switching (line selection) process in accordance an APS (Automatic Protection Switch) protocol for a transmission line, but performing, where the ring (UPSP) configuration is employed on the OC-n described above, selection processing of signals in the EAST/WEST directions. The RB 400 further has a time slot assignment (Add/Drop/Through: TSA) function 40b for low speed side lines. Consequently, the RB 400 can cope with various applications to the low speed side lines and allows connection to a high speed side line (high speed block 500).
The high speed block (HB) 500 includes an interface section 501 for interfacing with the high speed line side (a high speed circuit signal), and a TSA function 502 for performing time slot assignment (Add/Drop/Through) on the high speed line side and accommodates the low speed side lines by means of the TB 200 (RB 400) However, since the number of accommodated slots for the IF boards (cards) 300 (the number of the IF boards (cards) 300) for the low speed side lines (OC-n) which can be accommodated in one TB 200 (RB 400) has a physical restriction, for example, a plurality of (m) RBs 400 are accommodated for the high speed side line capacity (N channels) as shown in FIG. 52 so that all of the high speed side lines (for N channels) are accommodated in all of the RBs 400.
For example, if the high speed side lines have a ring configuration (UPSR) which handles signals (transmission frames) of the OC-192 (10 Gb/s) level, then the HB 500 is constructed with a signal processing capability of the OC-192 (10 Gb/s) capacity, and, for example, four RBs 400 having a signal processing capability of the OC-48 (2.4 Gb/s) level are accommodated in the HB 500. Further, four IF boards 300 are accommodated in each of the RBs 400 if the IF boards 300 are for the OC-12 (600 Mb/s) level, but one IF board 300, which is one fourth that in the case just described, is accommodated in each of the RBs 400 if the IF board 300 is for the OC-48 (2.4 Gb/s) level.
In short, a number of IF boards 300 corresponding to a transmission level applied to the low speed side lines equal to the number of slots corresponding to the processing capability (capacity) of the TB 200 (RB 400) are allocated to the TB 200 (RB 400). If it is assumed that the total signal capacity when the IF boards 300 for the OC-n level are accommodated in the full slots is the processing capacity of the TB 200, then when the IF boards 300 for the OC-(nxc3x974) level are accommodated, the number of slots in which IF boards 300 are accommodated is reduced to one fourth, thereby providing compatibility in mounting of various IF boards 300.
In particular, the ADM 100 described above is designed with the OC-n level set as a basic transmission level taking accommodation compatibility of the IF boards 300 for various transmission levels in the TBs 200 and the signal capacity for the high speed side lines (HB 500) (the processing capacity of the TBs 200) into consideration.
However, the ADM 100 described above has a subject to be solved in that, if IF boards 300 having a capacity smaller than the basic transmission capacity OC-n (for example, a capacity of an OC-n/4 or the like) are accommodated in a TB 200, then this directly results in reduction of the processing capacity of the TB 200.
For example, such an instance as shown in FIG. 54 is considered wherein the low speed side lines have a redundancy configuration (1+1 configuration having work lines/protection lines), and in a full slot accommodation condition, L IF boards 300 of OC-n for the work lines/protection lines (which are used for the EAST/WEST where a ring configuration is employed) are accommodated (mounted) in each of the TBs 200 (only two are shown in FIG. 54).
In this instance, while the total capacity of signals inputted to one RB 400 is OC-nxc3x97Lxc3x972 (in the case of FIG. 53, 4.8 Gb/s because n=12 and L=4), by a work/protection selection (APS) function, a transmission capacity equal to one half that mentioned above (OC-nxc3x97L: in the case of FIG. 53, 2.4 Gb/s) is selected by the RB 400 and interfaced to the high-speed block 500. In short, the communication capacity of one RB 400 when the RB 400 is interfaced (Add/Drop/Through processing) with the high speed block 500 is OC-nxc3x97L (in the case of FIG. 53, 2.4 Gb/s) (full condition).
Where the TB 200 has such a construction as described above, if, for example, each of the IF boards 300 is constructed (exchanged) for OC-n/4 [OC-3 (150 Mb/s) in FIG. 53] of the 1/4 transmission capacity, then the total capacity of signals inputted to one RB 400 is OC-n/4xc3x97Lxc3x972 (1.2 Gb/s in FIG. 53), and the signal capacity interfaced with the high speed block 500 is one half that given just above, that is, OC-n/4xc3x97L (600 Mb/s). In short, in this instance, the signal capacity of one RB 400 interfaced with the high speed block 500 is reduced simply to xc2xc (600 Mb/s)from the full condition (2.4 Gb/s) mentioned above.
In particular, in the TB 200 described above, if existing wiring line connections are diverted so as to deal with the IF boards 300 of various transmission capacities (so that the compatibility of each IF board 300 may not be lost), then as the transmission capacity of the IF boards 300 decreases from the basic transmission capacity OC-n, the processing capacity of one RB 400 interfaced with the high speed block 500 decreases [the density of the processing capacity to be actually interfaced decreases with respect to the processing capability (capacity) of the RB 400 which can be interfaced with the high speed block 500].
Here, in order to prevent such reduction of the processing capacity of the RB 400 as described above, the number of slots of the RB 400 for the IF boards 300 may be increased simply (for example, in the case of OC-n/4, a number of IF boards 300 equal to four times should be connected). However, this not only makes the unit scale very large, but also loses the accommodation compatibility (actually, since the number of accommodation slots of one RB 400 has a physical restriction as described hereinabove, such countermeasure as just described is substantially impossible).
It is an object of the present invention to provide an SDH transmission unit which can suppress reduction of the signal capacity to be interfaced with a high speed block while maintaining the accommodation compatibility with an IF unit (low speed line signal) of a transmission (signal) capacity smaller than a basic transmission capacity.
In order to attain the object described above, according to an aspect of the present invention, there is provided an SDH transmission unit, comprising a high speed block for accommodating high speed line signals handled by source network based on an SDH transmission system, and a tributary block for accommodating low speed line signals handled by a tributary network based on an SDH transmission system and having a transmission capacity lower than that of the high speed line signals and interfacing with the high speed block, the tributary block including a plurality of routing blocks each of which accommodates low speed line signals for a predetermined capacity and performing line selection processing for low speed line signals to be interfaced with the high speed block in accordance with a form of the tributary network, at least one of the routing blocks serving, when the low speed line signals accommodated therein do not fully occupy the predetermined capacity, as a master block which accommodates at least one of the other routing blocks as slave block in order to accommodate the low speed line signals accommodated in the other routing block.
In the SDH transmission unit having the construction described above, the master block (routing block) in the tributary block accommodates the other routing block (slave block). Consequently, a capacity portion of the master block by which the predetermined capacity is not satisfied can be made up for with the low speed line signals accommodated in the slave block. Accordingly, while the capacity of low speed line signals accommodated in one routing block is provided with flexibility (compatibility), even when the accommodated amount of low speed line signals in one routing block does not fully occupy the predetermined capacity, reduction of the capacity (hereinafter referred to as interface capacity) of low speed line signals to be interfaced with the high speed block can be prevented.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.